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Full text of "Alaskan glacier studies of the National Geographic Society in the Yakutat Bay, Prince William Sound and lower Copper River regions"

384                                 ALASKAN GLACIER STUDIES
section of the fiord is broadly U-shaped, the sides descending to a depth of 600 feet in three-eighths of a mile. For a width of 1| to l£ miles there is rather flat bottom at a depth of about 600 feet.
Submerged Hanging Valleys. All of the bays tributary to western Port Fidalgo are submerged hanging valleys. Fish Bay (PI. CXLVI), which is 90 to 96 feet deep at the mouth, hangs at least 500 feet; the bottom of the unnamed cove on the southern side of the fiord opposite Fish Bay is hanging a little less; while Landlocked, Boulder and Bowie Bays, and Snug Corner Cove hang still less above the bottom of the fiord, as ^would be natural with the greater size of these bays and of the tributary ice tongues which formerly occupied them. Port Fidalgo, 714 feet deep at the mouth, is itself a submerged hanging valley in relation to Prince William Sound, which in a distance of 2f miles reaches a depth of 1850 feet. This fiord, therefore, hangs over 600 feet above Prince William Sound, where the larger glacier presumably eroded more effectively than the Port Fidalgo Glacier. The channel between Goose Island and Porcupine Point at the southern entrance to Port Fidalgo, which has an average depth of less than 50 feet, and a maximum depth of 150 feet, shows a similar hanging relationship at both the northern and southern ends.
Tatitlek Narrows, with depths of 66 feet or less, hangs 90 feet or more above Boulder Bay, which itself hangs twice that amount above Port Fidalgo. Tatitlek Narrows also hangs above Valdez Arm (Fig. 28) at the northern end. Grant and Higgins state * that this strait lies in a belt of weak black slates and has an island of resistant diabase. These narrows constitute a submerged hanging valley of the third order, being discordant in relation to Boulder Bay which hangs above Port Fidalgo which, in turn, hangs above Prince William Sound.
Glacial Deposits. The deposits in the explored portion of this fiord are shown by the Coast Survey chart to be almost uniformly soft or sticky blue mud or fine sand. We liave little information about the glacial deposits above sea level along the sides of Port Fidalgo and the tributary valleys. There are small terraces of outwash gravel near the -entrance of the fiord. Bligh Island has "gravel deposits containing exotic materials," as Schrader and Spencer noted in 1900,a and there is also till with foreign materials on Goose Island, as we observed in 1910.
Port Gravina. Port Gravina, southeast of Port Fidalgo, is of smaller size, having a length varying from IS to 16 miles, as shown on different maps. It flares open rather •widely at the mouth, where it is half as wide again as Port Fidalgo. This fiord extends back into the Chugach Mountains, with peaks on either side rising to about the same heights as those around Port Fidalgo and with steep walls, those on the southern side rising to 2162 feet within half a mile of the shore.
Most if not all of the glaciers about the head of Port Gravina are small and only a few of them have even been indicated upon maps, two small ones, sketched from a distance, being shown on tiie Grant and Higgins map. None of them has been studied by any persons exploring Prince William Sound, and we observed them only from a distance near the mouth of the fiord. Glacial erosion and glacial deposits have not been investigated as yet, and there-are no soundings at Port Gravina, so that we lack all specific
i Op. cit., p. 60.
• Schrader, F. C. and Spencer, A. C., Geology and Mineral Resources of a Portion of the Copper River District, Alaska, House Doc. 646, 56th Congress, 2nd Session, Washington, 1001, p, 81.